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A Three-Dimensional Homology Model of the O-Acetylserine Sulfhydrylase-B from Salmonella typhimurium

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O-acetylserine sulfhydrylase (OASS) catalyzes the last step in the cysteine biosynthetic pathway in enteric bacteria and plants. The overall pathway involves the substitution of the β-acetoxy group of O-acetyl-L-serine with inorganic bisulfide. Two isozymes are present in S. typhimurium, the A- and B-isozymes, expressed under aerobic and anaerobic conditions, respectively. No crystal structure is presently available for the B-isozyme. Kinetic data indicate the catalytic mechanism of OASS-B is ping-pong, as found for the A-isozyme, but kinetic parameters and substrate specificity differ. In order to estimate whether structural differences may be responsible for the kinetic differences, a homology model was built using the structure of OASS-A as the template for the OASS-B model. The β- subunit of tryptophan synthase and cystathionine β-synthase were used for comparison. Differences between the OASS-A structure and the homology model for OASS-B are discussed.

Keywords: A-isozyme; Schiff base; Structurally conserved regions; asparagines loop; cysteine; homologous enzymes

Document Type: Research Article

DOI: http://dx.doi.org/10.2174/092986606774502126

Affiliations: Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Norman, Oklahoma 73019.

Publication date: January 1, 2006

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  • Protein & Peptide Letters publishes short papers in all important aspects of protein and peptide research, including structural studies, recombinant expression, function, synthesis, enzymology, immunology, molecular modeling, drug design etc. Manuscripts must have a significant element of novelty, timeliness and urgency that merit rapid publication. Reports of crystallisation, and preliminary structure determinations of biologically important proteins are acceptable. Purely theoretical papers are also acceptable provided they provide new insight into the principles of protein/peptide structure and function.
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